According to the National Institutes of Health, unregulated supplements now account for 20 percent of drug-related liver injuries. And it doesn't take too many pills to do damage, so Bonkovsky recommends completely avoiding supplements with green tea extract in them. If you have to take one, he says to limit it to no more than 500 milligrams (mg) catechins per day. This might be harder than it sounds, as some of the supplements the researchers tested had up to 700mg in one capsule and came with recommendations to take more several daily.